Friction materials for brakes, etc., are generally known to be produced by consolidating asbestos as a strength member, inorganic powders such as carbides, oxides, etc., as a friction-increasing member, carbon or graphite and the like as a friction-controlling member in a matrix of an organic resin binder, e.g., phenolics. See e.g., Takarada et al., U.S. Pat. No. 4,657,951 (1987). However, asbestos may well have health disadvantages in production and in use, and, in fact, the phasing out of its use is being encouraged by various authorities.
Numerous attempts have been made to replace asbestos with such materials as steel fiber, Kevlar fiber, cellulose fiber, etc. See e.g., Horiguchi et al., U.S. Pat. No. 4,722,949 (1988); Nakagawa et al., U.S. Pat. No. 4,672,082 (1987); Okubo et al., U.S. Pat. No. 4,477,605 (1984); Hamermesh, U.S. Pat. No. 4,476,256 (1984); Albertson, U.S. Pat. No. 4,403,047 (1983); Moraw et al., U.S. Pat. No. 4,384,054 (1983); Gallagher et al., U.S. Pat. No. 4,374,211 (1983).
However, results from such attempts have not been entirely satisfactory because of cost, handling and/or performance. For instance, a significant problem in the art is that the temperature resistance of the organic resin binder is usually low, typically being not greater than about 325.degree. C. Therefore, in order to bring about substantial improvements in the behavior of friction elements, binders having much higher temperature resistance must be developed. This requirement is more necessary in light of today's markets for high performance and high speed vehicles, to include airplanes, automobiles and trains etc.
Consequently, one of the most challenging tasks in the industry is to develop materials with not only a suitable low cost non-asbestos strength component but also a suitable binder such that their use in the production of friction elements can lead to retention of good friction characteristics at high temperatures. Heretofore, such tasks have been unfulfilled, and the art lacked the provision of these materials.